Due to the widespread usage of mobile devices, there is a constant motivation to improve on the performance of cellular communication networks. In the context of a service provider, it is desirable to have high data transfer rates, low bandwidth allocation which converts to lower licensing costs and yet still be able to support a large population of mobile stations within the coverage of a service centre without the need for massive changes to the existing cellular communication networks. An example of a cellular communication network with room for improvement is one employing Time Division Duplexing (TDD) and using Code Division Multiple Access (CDMA) scheme for transmission and reception of control and user data over the air-interface.
In order to provide high data rates to the users in a CDMA-based cellular mobile communication system, a high bandwidth is generally required. As licensed bandwidth is usually scarce and expensive to own, one solution to this dilemma is by reducing the cell size and increasing frequency re-use. To service an equivalent number of users/mobile stations while reducing the cell size, a proportional increase in the number of base stations to be deployed is required. However, this approach leads to higher capital investment and raising the overall inter-cell interference in the downlink direction. Alternatively, high data rates can be achieved by using faster modulation techniques that require a higher transmission power. But this has the similar effect of raising inter-cell interference level, which limits the applicability of CDMA systems since they are inherently interference-limited.
It is suggested that a good solution to the problems may be to adopt a multi-hopping approach between the mobile stations and the service centers. Based on this approach, the advantage offered by distributed multiple access schemes such as Opportunity Driven Multiple Access (ODMA) and Carrier Sense Multiple Access (CSMA) is that paths can be subdivided into shorter hops and frequency-reuse in the same cell can be easily implemented. However, such distributed Medium Access Control (MAC) schemes do not easily fit into the conventional cellular communication systems. Further, they may require dual protocol stack, another air interface, complicated billing and authentication and would be prone to attacks from malicious users since there is no central controller.
Infrastructure-based approaches on the other hand, where the BS acts as the overall coordinating entity, makes it simpler to implement multi-hop in the present cellular systems without the addition of another protocol stack. The billing and authentication are also a lot easier and it is not difficult to detect malicious users due to the presence of the BS acting as the overall controller. The only difficulty in infrastructure-based techniques, without frequency reuse in the same cell is that large number of intermediate hops for one communication link would require more wireless resources dedicated to one user in the absence of frequency reuse.
A prior art approach to incorporate multi-hopping capability into cellular communication networks is to employ a “dual-mode” interface strategy. This strategy proposes the use of a relaying mechanism using IEEE 802.11 wireless local area network communication standard, which is added alongside the conventional Global System for Mobile (GSM) communication network protocol on the Mobile Stations (MS). However, this method carries the drawbacks of requiring significant changes to conventional protocol stack implementations and the transmission and reception circuitries, both on the MS and Base Station (BS). The added complexity will also translate into substantially more complex MS and BS designs, and also result in costlier and bulkier MS handsets with higher form factor.
Another prior art approach is to use the concept of multi-hopping capability in ad-hoc networks. However, this method cannot be directly applied to cellular communication network to achieve effective multi-hopping results. The characteristics of ad hoc networks and cellular communication networks are significantly different to warrant different approach for each type of network to achieve multi-hop communication. There is no central device or infrastructure present in an ad hoc network such as a BS or an Access Point. Hence ad hoc network protocols if directly implemented over cellular networks cannot utilise the ability of the central controlling device namely the base station system. Furthermore, in contrast with cellular communication networks, the relay MS/node selection scheme and wireless resource assignment are not closely related and interdependent in ad hoc network routing protocols. The BS dictates the choice of relay MS, influenced by the current state of radio resources assigned. On the other hand, in ad hoc networks, these two aspects are completely independent of each other. This is mainly because Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) is used to access the shared channel, and that each node picks its candidate relay node autonomously without any central party involved.
Another prior art approach to incorporate multi-hopping capability into cellular communication networks is to use an ODMA-based multiple access scheme. However, this has the serious drawback in that it cannot be easily integrated into the present cellular CDMA system because ODMA operation would require certain amount of radio resources (codes, frequency channels, time-slots) to be reserved within the cell for the purpose of multi-hop communication. This method further mandates frequent beaconing from the BS which causes increased signaling overheads and raised interference level in the up-link direction. Moreover, the method described relies on each MS to probe the calling channel actively on a regular basis in order to obtain MS-MS connectivity information. This will drain MS's battery power unnecessarily and increase the up-link interference level due to constant probing of the calling channel, even if multi-hop configuration is not activated. The method also requires excessive overhead in terms of control messages as well as computation as it requires frequent route discovery and gradient calculation every time a new connection has to be started. In the case of large number of intermediate hops, the established routes are highly prone to route failures because as the number of intermediate MSs increases in the route, there would be an increased possibility of route failure due to the higher probability of intermediate relaying (data forwarding) MSs moving away from the multi-hop communication route.
In addition to the foregoing, to achieve the aim of incorporate multi-hopping capability into cellular communication networks, some prior art approaches have been attempted but failed because of numerous problems. For example, another prior art approach does not present any signaling mechanism and means for neighborhood discovery for the use of relay node selection. It only deals with the issues related to relay node selection and channel assignment. Further, the technique presented in this prior art requires the relaying channels to be borrowed from the neighboring cells. This has adverse effects on inter-cell interference. Yet another prior art approach also does not provide a signaling mechanism. Its intent is basically to control the interference in a permissible range by applying the CDMA system to signal collision in the conventional CSMA and TDMA multi-hop systems and to relax the hidden terminal problem.
Hence, it was with knowledge of the foregoing concerns that the present invention was conceived and has now been reduced to practice.